Amplifier employing semiconductors



June 1-, 1954 E. H. GROVER 2,680,159

AMPLIFIER EMPLOYING SEMICONDUCTORS Filed March v13, 1951 In venlor flP/CH. move-R generally supposed to Patented June I, 1954 EricHoughton'Grover, London,

England, assignor to International Standard'Electric Corporation,

New York,

N. Y., a corporation of Delaware Application March 13, 1951, Serial.No.215,227

Claims priority, application Great'Britain- March 21, 1950 6 Claims; (CL17 9171 The present invention relates toelectric amplifying devicesemploying semi-conducting materials, which have been called: forconvenience crystal triodes.

It is alreadyv known that certain crystalline semi-conducting materialsare suitable for use as point-contact rectifiers (generally known ascrystal detectors) and that such material maybe made'to act as anamplifier byv mounting a body of the material on, or in, a suitablemetal base or holder which makes electrical contact'with the bodyover-an extended area, and by providing it With two fine Wire electrodesor catwhisker arranged very close together incontact with the surface ofthe body. Bysuitably polarising the electrodes with respect-to the basethe device can be made to operate as an amplifier similarly'to athermionic valve, and for this reason the device has been called acrystal triode by analogy. However, the word triode is not intended tobe restricted to a device having just three electrodes, for as in thecase of thermionicvalves,"there may 'be additional electrodes employedfor control purposes.

In' such crystal triodes known hitherto, two

cat whisker electrodes are provided, andione of them, called the emitterelectrode, is polarised with respect to the' ducting material atpresent'k'nown for this purpose is germanium, and a suitable materialiorthe cat whisker is Phosphor "bronze.

The amplifying action in a crystal triodeis result from interactionbetween the collector-and emitter currents, and thecontrol of thecollector current bythe emitter current can therefore beimodified if theamount of inter-action can be modified;

The amount of interaction'between the collector-and emitter currents maybe increased by reducing the-cross-section of the semi-conductor at thepoint where the electrodes make contact, and by constraining thecollector and emitter currents so that'they both "flow mainly throughthe reduced portion of the semi-conductor. This is accomplishedaccording to the present invention by-providing an electric amplifyingdevice comprising a body of semi-conducting"material consisting of twomain portions connected by an intermediate portion of smallercross-sectional area than either of the main portions, a collectorelectrode-and an emitter electrode, each making rectifier contact withthesurface of the intermediate-portion of the material, two baseelectrodes in contact respectively with the two main portions; and meansfor separately biassing the collector and emitter electrodes each withrespect to a corresponding one-of the base'electrodes in such mannerthat both the emitter and the collector currents are constrained to-flowin the same part of the said intermediate portion.'

One way of carrying out-the invention is to mount thesemi-conductor on abase electrode or holder in the usual way and then to make-21 saw-cutthrough the holder and semi-conductor so that the latter is nearly, butnot quite, divided into two separate portions. The twocat whiskersmanner described in the specification of British Patent No; 682,206dated February 25, 1953 of K.-A.' Matthews'for Crystal. Triode-dividedBase Electrode with, however, the further requirement that across-blessing should be used, that cut," are constrainedto'flow largelyin the same direction' in the 'reducedcross section of thesemiconductor.

The conditions of the invention may be fulfilled in various other ways.For example, if thesawout be" made suf'nciently Wide; the two catwhiskers could be placed in contact with the semi-conductorat the bottomof the slot instead in a metal holder, and cutting a slot through theholder and semi-conductor to form the crevasse 4. The emitter andcollector electrodes 6 and i consist of cat whisker, shown as arrowheads. making point-contact with the surface of the semi-conducting bodyi at the narrow portion 5 just above the top of the crevasse i. The catwhisker should preferably be made from Phosphor bronze wire.

The emitter electrode 6 is biassed positively with respect to the baseelectrode 3 on the opposite side of the crevasse t by a source 3, havinga potential not more than about 1 volt. The source 8 is connected to theemitter electrode 6 through the secondary winding of an inputtransformer 9, the primary winding of which is connected to a pair ofinput terminals iii, which the signals to be amplified are supplied.

The collector electrode 1 is biassed negatively with respect to theother base electrode 2 by a source 12 having a potential which may beanything from 5 to so volts. The source 52 is connected to the collectorelectrode 3 through the primary winding of an output transformer [3, thesecondary winding of which is connected to a pair of output terminalsis, it which may be connected to a load circuit (not shown) to which theamplified signals are to be delivered.

The two base electrodes 2 and 3. are connected by a large blockingcapacitor it to bring them substantially to the same potential at signalirequencies.

For the above description it has been assumed that the semi-conductingmaterial is of the N- type, such as germanium, for example. If P- typematerial is used, each of the bias sources 8, i2 should be reversed. Abrief explanation of the difference between l and P- type semiconductingmaterial will be found in U. S. Patent No. 2,653,374 dated thews-C. deB. White for Electric Semiconductor, and assigned to the same assigneeas the present application.

It will be seen that with the arrangement shown the emitter andcollector currents are both constrained to flow in the portion 5 ofreduced cross-sectional area, and as each electrode is biassed withrespect to the base electrode on the opposite side of the crevasse 4,the two currents are forced to mix, and the degree of interaction isthereby increased.

Fig. 2 illustrates the second type of arrangement alluded to in theearlier part of this specification. Corresponding elements are given thesame designations as in Fig. l.

The crevasse or slot G is made wide enough to enable the electrodes 5and 1 to make contact with the semiconductor inside the crevasse 4instead of outside; otherwise the arrangement is essentially the same asshown in Fig. 1.

While the principles of the invention have been described above inconnection with specific embodiments, and particular modificationsthereof, it is to be clearly understood that this description is madeonly by way of example and not as a .7

limitation on the scope of the invention.

What is claimed is:

1. An electric amplifying device comprising a body of semi-conductingmaterial having two main portions and an intermediate portioninterconnecting said two main portions, said intermediate portion beingof a lesser thickness than either of said main portions to define achannel therebetween a collector electrode' and an emitter electrode,rectifier contact means for September 29, 1953, of K. A. Mateach of saidelectrodes each contacting the surface of said intermediate portion ofthe material, two base electrodes in contact respectively with the twomain portions, and means separately biassing the collector and emitterelectrodes each with respect to a corresponding one of the baseelectrodes in such manner that both the emitter and the collectorcurrents to the base electrodes are constrained to flow in the same partof the said intermediate portion, said contact means for the electrodesbeing spaced apart and so located that each engages the intermediateportion between the other contact means and that main portion to thebase electrode of which said other contact means is connected throughits bias means.

2. An electric amplifying device comprising a body of semi-conductingmaterial having a slot therein dividing it nearly but not quite into twoseparate portions, two base electrodes in contact respectively with thesaid two portions, a collector electrode and an emitter electrode,rectifier contact means for each of said electrodes, each of saidcontact means making rectifier contact with the surface ofsemi-conducting material on the narrow portion formed by said slot, andmeans for separately biassing the collector and emitter electrodes eachwith respect to one of the base electrodes, in such manner that thecollector and emitter currents to the base electrodes are constrained toflow in the same part of the said narrow portion, said contact means forthe electrodes being spaced apart and so located that each engages theintermediate portion between the other contact means and that mainportion to the base electrode or" which said other Contact means isconnected through its bias means.

3. An amplifying device according to claim 2 in which the collector andemitter electrodes and contact means comprise cat whisker makingpoint-contact with the surface of the said narrow portion on the faceremote from the end of the slot.

4. An amplifying device according to claim 2 in which the collector andemitter electrodes and contact means comprise cat whisker arranged inthe slot and making point-contact with th said narrow portion at theblind end of the slot.

5. An electric amplifying device comprising a body of semi-conductingmaterial provided with a transverse slot to divide said material into apair of main portions interconnected by arelatively thin bridge-likeportion, a base electrode maintained in contact with each of said twomain portions, a pair of cat whisker type electrodes maintained inengagement with the surface of said bridge-like portion in closelyspaced relation one to the other, and means for separately biassing saidcollector and said emitter electrode each with respect to one of thebase electrodes, whereby collector and emitter currents to the baseelectrodes are constrained to flow in substantially the same directionthrough the same part of said bridge-like portion, said cat whiskerelectrodes being spaced apart and so located that each engages theintermediate portion between the other cat whisker electrode and thatmain portion to the base electrode of which said other cat whiskerelectrode is connected through its bias means.

6. An electrical amplifyin device comprising a body of semi-conductingmaterial provided with a transverse slot to divide said material into apair of main portions interconnected by a relatively thin bridge-likeportion, a base electrode maintained in contact with each of said twomain portions, a pair of cat Whisker type electrodes maintained inengagement with the surface of said bridge-like portion in closelyspaced relation one to the other, the engagement point of each catwhisker with the surface of the bridgelike portion being closerto one ofthe base electrodes than the engagement point of the other cat Whiskerelectrode, means for biasing the emitter electrode with respect to thebase electrode fuithest removed therefrom to produce a current flowacross the bridge-like portion in a given direction, and means forbiasing the collector electrode with respect to the base electrodefurthest removed therefrom to produce a current flow across thebridge-like portion in the same direction as said given direction.

References Cited in the file of this patent UNITED STATES PATENTS

